Low-dose oral vitamin K to normalize the international normalized ratio prior to surgery in patients who require temporary interruption of warfarin.

BACKGROUND

In patients who require warfarin interruption before surgery and have an elevated international normalized ratio (INR) before surgery, low-dose vitamin K may normalize the INR in time for surgery.

PATIENTS AND METHODS

In a retrospective cohort study, we assessed the efficacy of 1 mg oral vitamin K to normalize the INR for surgery and whether resistance to re-anticoagulation occurs when warfarin is restarted after surgery. We studied a cohort of patients with an INR 1.4-1.9 on the day before surgery who received 1 mg oral vitamin K (vitamin K group), and a comparator group of patients with a normal INR (< or = 1.3) on the day before surgery who did not receive vitamin K (no vitamin K group). In both patient groups, we determined the proportion of patients with a normalized INR on the day of surgery and compared the mean INR after surgery when warfarin was resumed.

RESULTS

Of 43 patients in the vitamin K group, the INR was normalized (< or = 1.3) in 33 patients (76.6; 95% confidence interval [CI]: 64.1-89.4), and the INR was normal or near-normal (< or = 1.4) in 39 patients (90.7; 95% CI: 82.0-99.4) on the day of surgery. The mean (standard deviation) INR in the vitamin K and no vitamin K group 4-8 days after surgery was 1.75 (0.34) and 1.59 (0.36), respectively (P = 0.56).

CONCLUSIONS

In patients requiring interruption of warfarin for surgery, 1 mg oral vitamin K on the day before surgery can normalize the INR by the day of surgery and may not confer resistance to warfarin re-anticoagulation after surgery.